1. Field of Invention
Methods consistent with the present invention relate to a silicon stacked semiconductor package. More particularly, the method relates to a one time reflow process for through-silicon vias (TSV) interconnect 3-D packages. The method uses phase change materials for support pins that either vaporize or cure.
2. Background and Description of the Related Art
The relatively new through-silicon vias, or TSV, technique involves stacking chips/dies vertically in a package and then creating connections between the bottom of the top chip and the top of the bottom chip.
Conventional TSV packages contain interposers, spacers and/or gap control structures between the stacked dies and substrate. Reflow processes are performed to solidify solder bumps between the dies and substrate. In addition, often times, post-curing is required to completely harden the interposers, spacers and/or gap control structures. One problem with multiple reflows is that it may cause reliability issues with the solder bumps. Another problem is that multiple reflows increase the manufacturing time.
One convention method is disclosed in U.S. Pat. No. 7,160,757. In this patent, you position the interposer, first solder bumps and gap control structure on the substrate and then reflow to solidify the first solder bumps and the gap control structure. Next, you attach the die and second solder bumps on the interposer and reflow to solidify 2nd solder bumps. The gap control structure prevents the collapse of first solder bumps during the second reflow process. However, the method does not use epoxy support pins to stack chips on the substrate. Instead, it uses a combination of the interposer with solder bumps and gap control structures to stack the chip onto substrate. In addition, it does not use a one-time reflow process, rather separate reflows required to couple interposer to substrate and to couple flip chip onto interposer.
Another convention method is disclosed in U.S. Pat. No. 6,461,881. In this patent, spacers are provided on an active surface of a semiconductor device having solder bumps. The spacers can be made of partially cured epoxy. During reflow, the spacers maintain uniform distance between substrate and semiconductor device while the solder balls bond to the contact pads on the substrate. Post-curing completely hardens the spacers. However, the method uses spacers (support pins) to stack chip onto substrate, but does not use spacers to stack chip on chip. Also, it does not use a one-time reflow process. Instead reflow only causes solder ball attachment. In addition, post curing required to completely harden the spacers.
Another convention method is disclosed in U.S. Patent Publication No. 2006/0270104A1. In this publication, interposers are provided between two dies or between the substrate and die. The interposer can be made of an adhesive material. Heating cures the interposers (adhesive material), thereby coupling the two dies together. However, although the method uses adhesive interposers (support pins) to stack chip onto chip/substrate, it does not have a single reflow process for both solder ball attachment and curing of interposers.
Another convention method is disclosed in U.S. Patent Publication No. 2002/0074637A1. In this publication, flip chips are stacked such that the chips are electrically connected to one another by means of conductive bumps and conductive redistribution traces. Underfill material is provided between the chips to mechanically retain the chips in place. However, the method does not use support pins to stack the chip on the substrate or chip on the chip. Instead, it use underfill material to hold the chips in place. In addition, the reflow process only causes solder ball attachment, as no support pins are used.
It is an object of the invention to provide a process to reflow the solder bumps while keeping the stacked chips in alignment with each other.